Benedict created CASSANDRA-7032:
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Summary: Improve vnode allocation
Key: CASSANDRA-7032
URL: https://issues.apache.org/jira/browse/CASSANDRA-7032
Project: Cassandra
Issue Type: Improvement
Components: Core
Reporter: Benedict
Fix For: 3.0
Attachments: TestVNodeAllocation.java
It's been known for a little while that random vnode allocation causes hotspots
of ownership. It should be possible to improve dramatically on this with
deterministic allocation. I have quickly thrown together a simple greedy
algorithm that allocates vnodes efficiently, and will repair hotspots in a
randomly allocated cluster gradually as more nodes are added, and also ensures
that token ranges are fairly evenly spread between nodes (somewhat tunably so).
The allocation still permits slight discrepancies in ownership, but it is bound
by the inverse of the size of the cluster (as opposed to random allocation,
which strangely gets worse as the cluster size increases). I'm sure there is a
decent dynamic programming solution to this that would be even better.
If on joining the ring a new node were to CAS a shared table where a canonical
allocation of token ranges lives after running this (or a similar) algorithm,
we could then get guaranteed bounds on the ownership distribution in a cluster.
This will also help for CASSANDRA-6696.
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